A nice essay on the use of aerial photography during the Great War. Dan Gettinger writes on the precedents to contemporary “pattern of life” analysis carried out by the military. During World War I, analysts would use stereoscopes to hunt for visual clues about enemy movements on photos that were stitched together to form mosaic maps. The Royal Flying Corps took over 19,000 aerial photographs and collected a staggering 430,000 prints during the five months of the Battle of the Somme in 1916. This visual analysis upturned the horse as the dominant technology of reconnaissance:
Mosaic maps, which became an important tool throughout the war, were made by taking a series of overlapping vertical photos and aligning them together to create a comprehensive view of the enemy’s trench network. In the same way that an analyst today might use drone imagery to develop a “pattern of life” analysis based on behavioral signatures, photo interpreters in the First World War used stereoscopes—a device used to view two separate images—to make comparative studies of the imagery. “The interpreter is trained to know how things ought to look under all sorts of different conditions in a vertical photo,” wrote Harold Porter in Aerial Observation, in 1921. Interpreters looked for visual clues that might denote changes in the enemy’s position. For example, soil displacement or shadows could help identify trenches, embankments, artillery batteries and troop movements.